If you want to print on plastic, it’s challenging – most plastics are chemically inert and non-porous. That means you can apply all the ink you want; it’s not going to stick. In the 1950’s, a Danish engineer named Verner Eisby experimented with various techniques to overcome these challenges. He found that exposing the surface to be printed on to gas flame or sparks modified the surface to improve adhesion with the ink. It did so, though, in a crude & uneven manner, leaving imperfections & inconsistencies in the printed product. He then tried applying a high frequency corona discharge in a linear array. The plasma (gas in an ionized state) generated left a homogeneously treated surface on which to print, smoothly & evenly.
This has become the “industry standard” for many of the labels we see on commercial products, from shampoo & wine bottles on the grocery store shelf, to pennants & banners at public events. It also leaves the surface even more prone to picking up a static charge from rolling or unrolling, stacking, sliding, etc.
One of our customers makes a great many labels for all kinds of these commercial products, and uses an EXAIR Gen4 Ionizing Bar immediately prior to the printing operation:
Recently, I visited a local customer to look at a specific application. This company prints over 146,000 different labels on plastic film, paper and foil. They called because they were seeing several different static related issues during printing and stacking processes.
On their first application, involving a 60″ wide sheeter, they were having an issue with irregularities as the sheet travels over several rollers where it enters the print head of the machine, then is cut and stacked. At the time of the visit, they were using a competitor’s product after the printer but those products were not effectively removing the static. We were able to determine they were not working by using our Digital Static Meter which told us there was still a 2.7 kV charge after the treatment area. I recommended the customer replace the ineffective units with our 60″ Ionizing Bar. The Ionizing Bar produces a bulk of positive and negative ions to eliminate the surface static of an object when mounted within 2″ of the surface of the material. The bar features a mounting flange that would allow the customer to use the existing bracket for easy installation.
The second machine we looked at was a 42″ 3-sheet press. Our readings ranged from 4.2 kV on the top sheet, 1.4 kV middle sheet and 9.9 kV on the bottom sheet going into the press/print head and around 15.6 kV at the discharge. This unit also had another anti-static device taped in place but was clearly no longer operational. I again recommend the Ionizing Bar for this application as well. After speaking with the operator, he was saying he was also seeing an issue with the sheets lifting and trying to separate as they were being stacked. To remedy this problem I recommended using our Super Ion Air Knife at low pressure to blow ionized air from behind the sheet to help it float onto the stack and remove static at the same time. The Super Ion Air Knife is our Super Air Knife with the Ionizing Bar attached and is capable of dissipating 5kV in less than half a second.
Lastly, we looked at their smaller sheeting machine and on this unit we were seeing around 3.5 kV as they stack was fed into the feeder and 7-8kV at the end stacker. At the beginning of the process we noticed the customer was using an air blowoff on each side of the sheet stack to assist with lifting and getting some separation between the sheets for the mechanical lifter to feed the machine. At this area they were experiencing some issues as occasionally the lifter would pick up more than 1 sheet and cause a jam which shut the system down. It turns out the airflow across the sheets was actually generating a slight static charge as we were seeing higher readings around 4.2 kV. Since they were already using air, I recommended replacing these blowoffs with our Ion Air Jet. This would aid in reducing the static and result in a more effective separation between the sheets allowing for a cleaner lift. For the sheet itself, we would recommended the Ionizing Bar if they were able to mount within 2″ or the Super Ion Air Knife for further mounting distance.
We realize we can’t look at every customer’s process but any photos or videos you could share of your application, we would gladly review and make a possible recommendation. Please contact one of our application engineers for assistance.